Manufacture of picric acid



0. B. MACDONALD,

MANUFACTURE opmckgc ACiD. APPLIQATIO N {ILED JULY 10, 1517- 1,396,001, Imm; Nov. 1,1921.

ATT'Y',

I UNITED STATES PATENT OFFICE.

DAVID BAIRD MACDONALD, OF LEICESTER, ENGLAND.

MANUFAC JTURE OF PICRIC ACID.

(GRANTED UNDER plications in England Dec. 15, 1915, Patent v provementsin known No. 17525 of 1915; in England April 15, 191 6; in France Dec.12, 1.916; in Russia- Jan. 13/26, 1917, and in Italy Dec. 11, 1916,) ofwhich the following is a specification.

This invention relate to the manufacture of picric a'cid, its objectbeing to enable pure picric acid of a high melting point and free frommetallic contamination to be expeditiously and economically produced andWithout danger.

To this end the invention comprises imacid manufacture and preferablyalso makes use of an apparatus wherein the process of manufacture may becarried out in an economic manner as Wlll be hereinafter descrlbed.

The manufacture of picric acid has been attendant with danger to -agreater or lesser extent, but more often than not to a considerableextent, and one of the important re sults broughtabout by the presentinvention is'the elimination of danger. Further advantages resultingfrom the improve- I ments constituting the present invention arevolved,'falling temperature during facture of .cess of benzol has been aconsiderable reduction in the time inreaction, purity of picric acidproduced, and economy of the extracting agents employed.

The principal improvement included in the present invention consists, inthe manuplcric acid, in separating the picricric acid from the metallicimpurities pres; ent in the [product of nitration by adding benzolthereto at the, end of the nitrating operation.

It is, of course;

By adding benzol 'to the product of nitration, picr'ic acid is carriedinto solution but the metallic bodies do not pass into solution. Thenafter the exdriven oil, theresidue containing a'sufiiciency of benzol isallowed to crystallize, the crystals consist- Specification of LettersPatent.

Application filed July 10, 1917.

, ing of a loosely acid processes of picric known that picric acid issoluble in benzol.

Patented Nov. 1, 1921. Serial No. 179,775.

THE PROVIS IONS OF THE ACT OF MARCH 3, 1921, 41 STAT. L, 1313.)

linked compound of picric and benzol, portion of thesaid residue(consisting of the impurities) is drained ofi'. The benzol in thecrystalline compound is easily separated irernli1 the picric acidleaving the latter pure. of benzol in the manner and for the purposejust described, is applicable both in the known process which, consistsin treating mercury and nitric acid with benzol, and

also in the known process which consists in first sulfonating' phenoland treating this with sodium or potassium nitrate as will behereinafter fully set forth.

Further improvements comprised within :the present invention thenitrating process at a low temperature, and in restraining nitration anddriving off the nitro-benzol by means of steam.

part of the invention as by means of same the danger hitherto present atthis stage of the process is entirely eliminated. t is alo an importantfeature of the invention that the materials used as agents for producingthe picric acid or partly recovered after use and may be used again aswill be hereinafter described, thus making the process very economical.

To enable the invention to be clearly understood the same will bedescribed with reference form and arrangement of aid of which theprocess cally carried out.

to a convenient apparatus byv the may bQBCOIlOl'Ill- The apparatus isillustrated diagrammati- 90 cally in the accompanying drawing and,comprises mainly, a mixing pan 1 fitted with internal movable beaters 2and having a condenser tube 3, or other suitable cendensing means, inconnection returning thecondensate to the pan by a pipe 4 and, whenrequired, carrying it away by a pipe 5 to a receiving vessel 6. Themixing pan 1 is also provided with a gage glass 'or other known meanswhereby the level ofthe contents me be ascertained. Associated with themixing pan is a erystallizing pan 7, andintermediate of, the two pans isa condensing 0r distilling app s havi g a connection by a pipe 9 and theuncrystallizable 66 e improvement consisting in the use 60 consist incarrying out 70 may be wholly more specifically therewith, capable of(not shown) ture should not however, exceed 40 Benzol (rectified) 32parts The mercury is first dissolved in about 5 parts of the nitricacid, the solution is heated and added to the remainder of the nitricacid in the mixing: .pan 1 through the inlet 26 and mixed, the

with the mixing pan 1 and also by a pipe 10 with a storage tank 11.Means 12 and 13 for draining each pan are provided and a liquor tankdrainage from the crystallizing pan ,7. Each pan is jacketed, thejackets 15 and 16 having steam and water connections 17, 18, 19, 20, aconnection being provided from the mixing pan 1, to the crystallizingpan 7 by means of the pipes 21 to 25. The mixing pan and heater may bemade of acid proof iron but the crystallizing pan and connections 21 to25 and condenser 8 attached theret should be made of earthenware,aluminium or tin.

At the commencement of the process the materials may, for example, beused in the following proportions viz 4 parts (by weight) (by weight)(by weight) Mercury (metal) Nitric acid (s. g. l. 42) 100 partspreferably to boiling point benzol being. then added in a slow streamover about three hours, maybe added in three separate portions duringthis period.

the heaters 2 and as the temperature has a the process, the pan water inthe jacket 15 to maintain the temperature of the mixture atapproximately 35 C. The purpose of this low temperatureis to producelargely, during the reaction, dinitrophenol in the first instance whichlater on, when the temperature is raised, is converted intotri-nitrophenol. The tempera- C. since at a higher temperature than thisa basic mercuric picrate is liable to form, the yield of picric acidbeing thereby reduced. At a higher temperature than 40 C. picric acidwould be formed, but since the reaction process extends over a period of8 to '10 hours if the higher temperature is maintained, the picric acidformed will be largely split up 'into oxalic acid and various otherbodies.

By carrying out the reaction during nitration at the comparatively lowtemperature specified the formation of basic mercuric picrate isobviated and consequently the anger of explosion at this stage iseliminated.- A thermometer of suitable type is ture.

After a period of about ten hours has been allowed for the, reaction totake place-during which the nitro-benzol and nitric acid which volatlhze'are collected through the 14: is arranged to receive theoralternatively it I 1 is heated by warm condenser tube 3, condensed andreturned by the tube 4.to the pan-the temperature of the liquid israised to boiling point and maintained thereat for a period of about onehour. The nitro-benzol and nitric acid driven off during ebullition iscollected through the condenser tube 3 and directed by the pipe 5 intothe receiving vessel 6 and reserved for further use as will be explainedlater herein.

A jetof steam (preferably dry) is now blown through the liquidconveniently by a pipe 28 (or the spindle 29 ofthe heaters may be hollowto admit the steam) during which operation also the volatilizednitrobenzol is collected through the condenser tube 3 and carried off tothe receiving vessel 6 just referred to. Preferably the steam is blownthrough the liquid at or about the same time that the temperature of thelatter is raised as aforesaid but it may be intro duced at an earlier orlater stage if desired.

The use of steam forms an important paiit of this invention seeing thatit is one of the contributory features to the danger from the process.By introducing steam into the mass at that stage in the'nitrationprocess when it is desirable that -further nitration should beprevented, the extreme oxidation of the phenolic bodies into oxalic acidand the like which will take place During the period of reaction themixture unless the'strong nitrating agent is diluted, is obviated. Thesteam therefore constitutes a diluting or restraining agent and at thesame time carries off the nitro-benzol and an mono-nitro-phenol whichmay be volatile at the temperature employed, thus facilitating thepurification and final crystallization of the picric acid.

When practically all the nitro-benzolhas been removed from the mixtureand collected in the manner described, the steam is shut off. Freshbenzol (about 60 parts) is then added to the mixing pan, and after thecontents have been thoroughly mixed for about fifteen minutes themixture is allowed to settle, whereupon the benzol portion containingcrude picric acid is tapped off at 21 and run into the crystallizing pan7. I

The crystallizing pan is then steam heated by the jacket 16 whereby thebenzol is volatilized and by passing through the condensing coil 8 isdistilled back through the pipe 9 into the mixing pan 1.

The contents of this pan 1 are again thoroughly mixed, allowed tosettle, and the benzol again tapped off at 22 and run into the crystallizing, pan 7. The crystallizing pan is then heated to drive offabout half the benzol which is distilled by the condenser 8' and carriedby the pipe 10 to the storage tank 11 and reserved for further use, andthen the said pan .is waiter cooled by the jacket 16 to causecrystallization of the contents, The mother liquor is drained off fromthe crysta llizing pan by the connection 13 and collected in the. liquortank 14 the said liquor containing some picric acid,orthomononitrophenol, nitro-benzol and benzol.

About-3O parts of fresh benzol are now added to the contents of thecrystallizing pan 7 by means of the inlet 7, the pan is heated, todissolve the contents after which it is cooled to cause crystallization.When crystallization has taken place the liquor is drained off at 13 andcollected in the liquor tank 14.

Samples of crystals (which contain combined benzol) are now taken fromthe crystallizing pan, and the benzol is dissipated with heat of say awater-bath. The residue consisting of picric acid is tested for meltingpoint, which, with two crystallizations as described, should be 122 C.sharp.

Upon the melting point being found correct the crystallizing pan isagain heated by a gradually increasing temperature up to about 100 C.,to drive off the last traces of the benzol, ,the remaining contents ofthe pan being purepicric acid. The crystallizing pan is fitted with anobservation glass 30 which may be removed for sampling the crystals.

Y The remaining contents of the mixing pan '1 are now heated until-- allthe nitric acid and moisture are driven off and collected by thecondenser tube 3 into the receiving vessel 6; leaving practically drymercury salt in the pan. It is preferable to carry out this evaporationat a low temperature by means of a vacuum.

When starting a fresh batch, a portion of the nitric acid charge isadded to the mercury salt and warmed in the mixing pan 1 until solutionis effected, then the remainder of the nitric acid is added and theprocess is continued as before, no further mercury being required,although it may have to be renewed from time to time on account ofaccumulating iron salts. v

The time occupied bythe complete process is approximately 24 hoursalthough it may be less of course when one of the crystallizations isomitted.

The picric acid left in the mother liquor may, if desired,be recoveredfrom this by prolonged crystallization and if the residual liquor istreated with a jet of dry steam, which removes the nitro-benzol andbenzol, the orthomononitro-phenol will be left in a condition suitablefin dye manufacture.

This nitric acid and nitro-benzol (.Olllvttd in the receiving vessel 6may be separated in any known manner and collected in tanks 31, 32 andthe nitric acid may be revivified or concentrated and used again in thisprocess.

The benzol distilled into the storage tank 11 may also be used again.

Therefore, in so far as the materials emtilling and collecting orreturning to the mixing pan the benzol from the crystallizing pan 7, andseparating from the remaining contents in the mixing pan the dry mercurysalt, be recovered and used again the process may be said to beeconomical.

As the process is carried out in a closed apparatus and the temperatureduring the process has a natural tendency to fall all danger iseliminated, in addition to which the necessity for personal attention isconsiderably reduced.

Obviously it will depend upon the quantity orlevel of the solution inthe mixing pan as to which of the outlets 21 22 or 23 is used fortapping off at each operation. A branch 3" on the condenser tube 3 maylead to a suitable acid tower so that any nitrous fumes given oil may beoxidized and returned to the mixing pan 1.

-Hitherto, therehas been attendant with the process of producing picricacid which consists in first sulfonating phenol and then treating thiswith sodium or potassium nitrate in such a manner that picric acid isformed together with considerable quantities of sodium or potassiumsulfate or acidsulfate or mixture of same, great difficulty inextracting the picric acid; also considerable waste of same in theprocess of'washing as usually carried out. These disadvantages have beenso pronounced as to retard somewhat the development of processes ofmaking picric acid with, nitrates of the alkalis.

' By the use of benzol according to the present invention the aforesaiddisadvantages are overcome. This is achieved by treating the mixture ofpicric acid and sulfate, or .the acid-sulfate of the alkalis, accordingto the process used, with benzol.

By treating the aforesaid mixture with benzol in a suitable a )paratusin the presence of mineral acid, such as sulfuric acid) and with orwithout added waterat a suitable temperature above the freezing point ofbenzol, the picric acid together with any organic byproducts passes intosolution.

According to an example of the process, 100 parts of phenol may beheated with say 1000 parts of concentrated sulfuric acid for say twohours at a temperature of 170 this producing phenol-di'sulfonic acid.

To this 96 parts of dry powdered hile saltpcter are added and heated at140 (7. pro ducing nitro-phcnol-di-sulfonic acid. This is diluted with320 parts of water and heated to 8090 with 244 parts of (bile saltpeter,the temperature being allowed to reach 40 C., approximately 400 parts ofbenzol.

are added thereto and the solution of pie- 'ric acid in benzol is tappedoff and run into the crystallization pan and then treatedin the mannerpreviously mentioned, the benzol being driven offand condensed andreturned to the mixing pan or collected in the storage tank leaving thepicric acid in the pan 7.

If other organic bodies are present at this stage a suitable quantity ofbenzol is left in the picric acid in the crystallizing pan. This pan iscooled and the contents allowed to crystallize in the form of a loosecompound of picric acid and benzol from which is subsequently drainedthe uncombined benzol together with such impurities as may be present.The picric acid may be recrystalized from further benzol if desired.

In the process just described, instead of the sodium nitrate thecalculated quantity of potassium nitrate may be used.

The invention is-not to be confined to. the hereindnentioned quantitiesand details as these are given only as examples and may be varied iffound necessary or desirable.

In the apparatus employed instead of tapping into solution off from' themixing pan it may be separated by decantation or siphoning and theinvention is not to be restricted to the. precise construction. andarran ement dation and driving off the nitro-benzol by means of steamsubstantially as and for the purpose herein described.

In testimony whereof I have signed my name to this specification in thepresence of two subscribing Witnesses.

DAVID BAIRD MACDONALD. ,Witnesses R. W. C. TAYLOR,

GEORGE LESTER.

